The vials of smallpox, believed to have been from the 1950s, were immediately secured in a containment laboratory in Atlanta. Scientists discovered the vials in a Bethesda, Maryland, storage room when preparations were being made to move to the FDA’s main campus.

“There is no evidence that any of the vials labeled variola has been breached, and onsite biosafety personnel have not identified any infectious exposure risk to lab workers or the public,” the CDC said in the release.

Additional testing, expected to take about two weeks, will be conducted on the variola to determine if it can grow in tissue culture, after which the samples will be destroyed.

The World Health Organization, which has been invited to participate in the investigation of the smallpox vial discovery, has designated only two laboratories — one in Atlanta and one in Russia — as the only two such sites where smallpox can be stored.

“The WHO oversees the inspection of these smallpox facilities and conducts periodic reviews to certify the repositories for safety and security,” according to the CDC.

The CDC’s Division of Select Agents and Toxins and the Federal Bureau of Investigation are also participating in the investigation as to how the vials were found to be in a nonsanctioned laboratory.

The CDC said the variola virus could be used as an agent of bioterrorism. The disease can’t be prevented other than through vaccination.

The last reported case of smallpox in the U.S. was in 1949 while the last naturally occurring global case was in Somalia in 1977.